Given the rapid climb of conventional energy costs and given the growing concerns about the environment, the interest in alternative energy sources that are both renewable and clean is growing steadfastly. In this regard, solar power is considered to be one promising solution since it is not only clean and renewable, but also plentiful: every day the sun hits the earth with roughly 20 000 times the current daily energy consumption by humankind.
The two main technologies currently used to harness the power of the sun are Concentrating Power Systems (CPS) and Photovoltaic (PV) Panels. Concentrating Solar Power (CSP) systems use lenses or mirrors and sun tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. While these systems may be very efficient, they are also cumbersome and are thus typically installed on open ground, thus monopolizing expensive land space. Photovoltaic panels are assemblies of photovoltaic cells (also called solar cells or photoelectric cells), which are electrical devices that convert the energy of light directly into electricity by the photovoltaic effect. They come in the form of thin rectangle boxes that can be assembled into grids of various sizes. Given their smaller size and weight, they can be installed on a broader range of locations relative to CSP systems.
PV panels are commonly found over roofs because their height usually provides themes with better exposure to sun rays than open ground. Another advantage resides in the fact that rooftops are often unexploited otherwise, so that using this empty or “wasted” space can thus free open ground for better use. Furthermore, since roofs are by their nature part of buildings, hooking the PV panels directly to the existing electric facilities is often easier than with an open ground PV installation requiring some excavation work, foundation building and more complex outdoors wiring.
A roof construction typically consists of footings of various shapes and an outer weatherproof skin or covering. A simple ridged roof may consist of declined rafters that rest on vertical wall plates on top of each wall. The top ends of the rafters meet at the horizontal ridge plate or ridge beam. Horizontal purlins are fixed to the rafters to support the roof covering. Heavier under purlins are used to support longer rafter spans. The beams or ceiling joists, are connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength.
Corrugated sheet metal panels are commonly used as sloping roof weatherproof covering material. A single corrugated sheet metal panel is typically composed of a series of large web sections separated by a series of thin raised rib sections, each panel starting and ending with a rib section. When assembled to form roof covering, the ending rib of the new panel being installed overlaps on the ending rib of the panel already in place, thereby providing a gravity borne mechanical seal. The sheet metal panels are fixed to the roofs furring strips or studs using lag screws placed over the ribs at sheet junction points to minimize leakage risks, the water being drained over the lowered section.
On most roofs, the trusses are spaced every 24 inches. On metal roofs, the metal sheets are screwed to the structure on the ribs to prevent leak problems. The ribs of a sheet metal roof are in many cases spaced at 9 inches. A metal sheet is usually 36 inches wide. The probability that the ribs of the sheet metal roof will be directly over a truss (rafters) is low. To ensure a good long term seal, the lag bolts of the mounting system have to be secured on top of sheet metal ribs. The number of roof clamps to be installed depends on the type of building structure and the size of the furring strips (studs). Furring strip studs are weaker than trusses, so more fixtures must be added accordingly. There are lots of different metal sheets with different rib shapes and sizes. Proper sealing with a good structural integrity is important. The metal sheets are usually fastened to furring strips or studs. These wood members are not always the same size and each consecutive pair thereof is not spaced the same distance relative to one another.
Installing PV panels on sloping roof can be challenging because not only are roofs generally hard to access and dangerous to operate on by workers, but they are also exposed to weathering elements, including heavy winds, rain or snow, and large temperature gradients. Such installations must therefore take into account of not only the weight of the panels and their support structure, but of the combined loads imposed on the roof infrastructure such as the wind load, the rain and snow loads, other equipment load, and so forth.
Furthermore, PV structural elements of the panels tend to accumulate heat when exposed to sunlight. Unfortunately photovoltaic performance degrades as their temperature increases. Excess heat can also lead to sheathing material degradation that can reduce the roof effectiveness in protecting the building. For example, excess heat could lead to sheet metal paint degradation, exposing the metal to corrosion, thus compromising the roof's integrity. Excess thermal loads can be mitigated by providing spacer elements between the PV panels and the rooftop sheathing, so that natural ventilation occurs.
However, it was found by the present inventor that such prior art spacer elements provided overall weak ventilation capabilities around the PV panels overhanging rooftops.
Finally, installing any equipment on a roof can increase water leakage hazard inside the building because of water, snow or ice accumulations that can lead to water levels rising above their usual levels, therefore exposing sections of the roof normally not or less exposed to water. In the case of sloping sheet metal roof, this could be water rising above a sheet metal rib with improperly sealed fastening screws. Moreover PV installations will likely require additional holes to be pierced across the roof's sheathing material in order to reach the underlying infrastructure to insure the proper anchoring of the PV panels support assembly. This evidently increases the risks of water leaking into the building.
It is recommended to wear gloves during PV installations, to prevent electrical hazard accidents.